Optical fibers are used in a wide variety of applications such as communication equipment, sensors, lighting, ornamentation, and displays. Glass optical fibers have excellent optical transmission properties in a wide range of wavelengths; however, their processability and mechanical characteristics are not so excellent. By contrast, plastic optical fibers are structured, for example, by coating the outer periphery of a core made of a highly transparent resin such as polymethyl methacrylate with a highly transparent resin having a refractive index lower than that of the core. Compared with glass optical fibers, plastic optical fibers are excellent in processability, flexibility and the like. Moreover, the transmission distance of plastic optical fibers has been further extended by the improvement of production technologies in recent years, and their application range is being expanded.
Generally speaking, optical fibers are not used by themselves, but are usually used as optical fiber cables, which are formed by coating optical fibers with thermoplastic resins or the like to provide mechanical characteristics, flame retardancy, heat resistance and so forth. Especially, since regulations on flame retardant properties of plastic products have become stricter recently, optical fiber cables are required to have excellent flame retardancy.
To provide flame retardant properties for optical fibers, Patent Literature 1, for example, proposes optical fiber cables formed by coating chlorinated polyethylene on plastic optical fibers.